The present invention relates to permanent or flying splices between sheet materials of the butt, overlap and in particular staggered overlap kind, a splicing tape for use in producing such splices and methods of using the splicing tape in producing butt, and overlap, particularly staggered overlap splices.
In this application and merely for clarity purposes, the leading end and edge of sheet material on a roll is considered to be the last quadrant of sheet material exposed on the outside of the roll, i.e. the section 32 of sheet material shown in FIG. 3B from the imaginary line A--A' to the edge 35. The underlying winding of such a roll is then the piece of sheet material on which the leading edge 35 rests, from A--A' through 360.degree. to A--A' again.
Two common types of splice are known for webs of sheet materials. Firstly, there is a permanent splice for joining the leading edge of one roll or part roll to the trailing edge of a further roll or part roll. The permanent splice should provide a flexible strong connection between the two webs and should maintain substantially all of the properties of the sheet material, for example if the sheet material is paper which can be printed or coated, the permanent splice is preferably, thin, flexible, printable, coatable and should also have the same repulpable properties as paper. Conventional splicing tapes and splices do not generally meet all of these requirements. Further, when joining part rolls the second roll is normally wound back onto the first roll in order to produce a complete roll and the permanent splice is then located somewhere in the middle of the new larger roll. This splice is subject to high pressures caused by the winding tension and it is important that no adhesive materials are present either on or near the splice or bleed out of the splice during storage which could adhere layers of sheet material together or damage or obstruct printing machinery.
A typical permanent butt splice is shown in FIG. 1A. Such a splice can be manufactured using a splicing tape as shown in FIG. 13 and described in WO 90/08032.
A permanent overlap splice is also known as is shown in FIG. 1B and is known in a modified form from WO 93/12025. Here the leading and trailing edges 3 and 4 of the first and second rolls are joined together by a double sided tape of the kind shown in FIG. 14. With reference to FIG. 3B the last sheet layer 32 of the roll 30 is secured by small adhesive tabs 33 applied on both sides of the roll 30. One of the release foils 10 (or 11) is then removed from the double sided tape 24 to expose the pressure sensitive adhesive 2A (or 2B) and the tape is applied across the width of the last sheet layer 32 of the roll. The excess of the leading edge is folded back against the double sided tape and is creased and torn off so that the final leading edge 35 abuts the double sided adhesive tape 24 as shown in FIG. 3B. In this condition the roll may be stored until a splice must be made. In order to complete the splice the remaining release foil 11 (or 10) is removed thus exposing the pressure sensitive adhesive 2B (or 2A) and the trailing edge of the second roll is then applied to the exposed pressure sensitive adhesive. The excess of the trailing edge is folded back to the adhesive join and is creased and torn off in the same way as described above with respect to the leading edge of the first roll. The splice now appears as in FIG. 1B.
This type of splice has a disadvantage that there is a considerable step at the change from the sheet material 3 or 4 and the splice itself when compared with the butt splice shown in FIG. 1A. This step can disrupt the printing process. Further, there is the possibility of the adhesive bleeding out of the splice or bleeding through the paper if placed under pressure. Additionally, the webs of sheet material may move relative to each other when tension in the web puts the splice in shear. If movement occurs during multiple pass printing the alignment in successive printing stages is disturbed resulting in inferior quality. Any relative movement is likely to release adhesive with the serious consequences mentioned above. To prevent this movement an additional adhesive tape 6' is sometimes applied along the edge of the splice as shown in FIG. 1B. This improves the strength of the splice but increases its thickness still further.
Since a paper manufacturer is often held liable by the printer for damage caused by the splice it is desirable to provide a reliable splicing method and splice which does not affect the printing process. In particular a sheet surface with exposed aggressively tacky adhesive is considered not to be machine printable.
In order to reduce the step at the splice, a staggered overlap splice as shown in FIG. 1C has been proposed in EP-0555772 which can also be produced with a splicing tape shown in FIG. 15. The splice in accordance with FIG. 1C may still suffer from the bleeding out problems of the overlap splice shown in FIG. 1B and has the further disadvantage that the leading edge of the first roll must be cut to a straight line before application of the tape rather than being able to tear off the leading against the adhesive join.
Splicing can also become necessary when insufficient sheet material is left on one drum. Webs from two drums must be attached together.
Flying splices are usually temporary splices made at machine running speeds between rolls when it is undesirable to stop the machine, e.g. during coating or printing. The surface speed of the roll can be 1000 or even 2000 meters per second. Conventional way of making a flying splice can be understood from FIG. 3A with reference to U.S. Pat. No. 4,564,150 or CA-2025473. Double sided adhesive tape 24 similar to that shown in FIG. 14 is applied to the last layer 32 of a roll 30 of sheet material in the form of a W, a V or any other suitable arrangement. The last layer 32 of sheet material is torn off against the adhesive tape 24 leaving small wings 23 which are secured by small pieces of adhesive tape to the underlying winding 31 of sheet material. The adhesive tabs and the small wings 23 are important to hold down the noses of the last layer 32 of the sheet material when the roll is travelling at machine rotation speeds. It is important that air cannot enter beneath the leading edge 35 of the last sheet layer 32 which would result in the roll unwinding itself at very high speeds which could cause damage to the equipment and danger to the operators. In order to prevent air entering beneath the leading edge 35 of the last sheet layer 32, small adhesive tabs are sometimes applied not only at the noses of the leading edge but also along the diagonal edges of the leading edge 35. Completion of the splice is described in U.S. Pat. No. 4,564,150.
The final splice appears as in FIG. 2B. The leading edge 3 of the new roll is attached to the trailing edge 4 of the old roll by means of the double sided tape 1, 2A, 2B and the excess of the trailing edge left after cutting is indicated by 8.
It is possible to make a flying butt splice with a butt splicing tape of the kind shown in FIG. 13. The final splice is shown in FIG. 2A in which the leading edge of the new roll has been attached to the splicing tape via the pressure sensitive adhesive 2B and the trailing edge of the old roll has been attached to a large area of pressure sensitive adhesive 2A leaving the excess of the trailing edge 8 to trail behind.
Although the low step profile of the butt splice would be preferred for both permanent and the flying splices, several disadvantages with the application of the tape have resulted in this tape not being widely used for either permanent or flying splices. Firstly, a tape of the kind shown in FIG. 13 must be stretched across the width of a roll which may be 4 to 10 meters wide with the non-adhesive side of the backing 1 adjacent to the roll. This is usually done by two or more operators who provisionally may tape the roll into its final position using small pieces of adhesive tape. Such a procedure is time consuming and there is the danger that the small pieces of tape are not removed after application of the tape. Secondly, adhesive may be transferred from the tabs to the sheet material which can result in subsequent bonding between layers of the sheet material or fouling of printing machinery. Thirdly, flying butt splices have not found favour because it is necessary to lift the leading edge of the new roll in order to apply such tapes. This lifting of the leading edge allows air to enter between the leading end 32 of the new roll and the underlying winding 31 of the roll and thus there is an increased danger of the leading edge lifting off from the roll when it has reached machine speeds. The same problem of lifting the leading edge may also occur if a staggered overlap flying splice were to be made with the splicing tape shown in FIG. 15.
In DE-A-4033900, a modified flying butt splicing tape is proposed. This splice tape, therefore, leaves an exposed surface of adhesive on the underlying winding of the first roll at a distance of approximately one circumference of this roll from the actual splice. This exposed adhesive layer is capable of picking up sheet remnants or attaching itself to other objects or parts of the machinery which can disrupt smooth operation, in particular machine printing. Further, some of the materials used to make the splice could be environmentally improved. A further disadvantage is that after positioning on the roll the splicing tape is not repositionable.
None of the above mentioned conventional splicing tapes provide a low profile tape with the facility to releasably attach the tape to the underlying winding while leaving the undelying winding non-tacky when the splice is complete.